es2/blocksize_KB is a SAP Parameter attribute which is used to control Block size for extended memory information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This value specifies the size of blocks into which the extended memory
is organized. If a user context requests memory from the extended
memory, one or more blocks of this size are provided from the extended
memory pool.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.